In digital broadcasting (such as terrestrial digital broadcasting) of standards such as the Association of Radio Industries and Businesses (ARIB), the Advanced Television System Committee (ATSC), and the Digital Video Broadcasting Project (DVB), viewers can only watch programs without watching commercials. For example, viewers can avoid watching commercials by switching to another channel only during commercial breaks. In the present business model, if viewers do not watch commercials, sponsors may stop providing funds to create TV programs. As a result, the number of good quality programs may be reduced.
Accordingly, in recent years, for example, a technology has been proposed to insert an Entitlement Control Message (ECM) including a work key (key information for descrambling) into a commercial portion that forms a transport stream (TS) transmitted by being scrambled. With such a technology, viewers are made to watch commercials at least once.
For example, in a video-on-demand (VOD) system, a method is disclosed for inserting commercial related information on a commercial while a TV program is distributed. In this method, a user terminal stores a TV program in a storage unit and also stores commercial related information in the storage unit. When a commercial is being skipped, the user terminal reads out the commercial related information from the storage unit and displays the information with the program.
However, in the conventional technologies described above, viewers are not made to watch information on commercials, if the channel is switched to another channel only during commercial breaks. More specifically, in digital broadcasting, for example, if the channel is switched to another channel in real time only during commercial breaks, the commercials are not played back on the receiver side. If the channel is switched to another channel in real time, the commercial related information inserted into commercials or a TV program is not be stored in the storage unit. Accordingly, the problems described above cannot be solved by conventional technologies.
In the technology described above in which an ECM including a work key is inserted into the TS to be transmitted, it is assumed that the broadcast data is transmitted by being scrambled. Accordingly, it is not applicable when the broadcast data is transmitted without being scrambled.    Patent Document 1: Japanese Laid-open Patent Publication No. 2002-51321    Patent Document 2: International Publication Pamphlet No. WO 03/079690